Funtion

Question 1

WHAT TYPE OF FUNCTION?

function isEven(num) {  
  return num % 2 === 0;
}
isEven(24); // => true  
isEven(11); // => false

Answer 1

FUNCTION declaration

Question 2

what are the 6 types of functions?

Answer 2

Function declaration
Function expression
Shorthand method definition
Arrow function
Generator function
Function constructor

Question 3

console.log(typeof hello);    // => 
function hello(name) {  
  return `Hello ${name}!`;
}

Answer 3

‘function’

Question 4

console.log(hello.name)       // => 
function hello(name) {  
  return `Hello ${name}!`;
}

Answer 4

‘hello’

Question 5

function hello(name) {  
  return `Hello ${name}!`;
}
console.log(hello('Aliens')); // =>

Answer 5

‘Hello Aliens!’

Question 6

WHAT TYPE OF FUNCTION?

function sum(a, b) {  
  return a + b;
}
sum(5, 6);           // => 11  
([3, 7]).reduce(sum) // => 10

Answer 6

A regular function

Question 7

_______means that you declare the function once and later invoke it in many different places.

Answer 7

Regular function

Question 8

the _________ in a statement always starts with the keyword function.

Answer 8

function declaration

Question 9

WHAT TYPE OF FUNCTION?

var isTruthy = function(value) {  
  return !!value;
};

Answer 9

function expression

Question 10

(function() {
  'use strict';
  if (true) {
    function ok() {
      return 'true ok';
    }
  } else {
    function ok() {
      return 'false ok';
    }
  }
  console.log(typeof ok === 'undefined'); // =>

Answer 10

true

Question 11

(function() {
  'use strict';
  if (true) {
    function ok() {
      return 'true ok';
    }
  } else {
    function ok() {
      return 'false ok';
    }
  }

console.log(ok()); //
})();

Answer 11

Throws “ReferenceError: ok is not defined”

because the function declaration is inside a conditional block.

Question 12

(function() {
  'use strict';
  var ok;
  if (true) {
    ok = function() {
      return 'true ok';
    };
  } else {
    ok = function() {
      return 'false ok';
    };
  }
  console.log(typeof ok === 'function'); // =>

})();

Answer 12

true

Question 13

HOW TO FIX THIS?

(function() {
  'use strict';
  if (true) {
    function ok() {
      return 'true ok';
    }
  } else {
    function ok() {
      return 'false ok';
    }
  }

console.log(ok()); // Throws “ReferenceError: ok is not defined”
})();

Answer 13

make “function ok” into a function expression

Question 14

The 3 things a function expression creates a function object that can be used in different situations:

Answer 14

1. Assigned to a variable as an object count = function(…) {…}
2. Create a method on an object sum: function() {…}
3. Use the function as a callback .reduce(function(…) {…})

Question 15

var getType = function(variable) {  
  return typeof variable;
};
getType.name // =>

Answer 15

empty string

Question 16

var getType = function funName(variable) {  
  console.log(typeof funName === 'function'); // => true
  return typeof variable;
}

console.log(getType(3)); // =>

Answer 16

‘number’

Question 17

var getType = function funName(variable) {  
  console.log(typeof funName === 'function'); // => true
  return typeof variable;
}

console.log(getType.name); // =>

Answer 17

‘funName’

Question 18

var getType = function funName(variable) {  
  console.log(typeof funName === 'function'); // => true
  return typeof variable;

console.log(typeof funName === ‘function’); // =>

Answer 18

false

Question 19

____________ definition can be used in a method declaration on object literals and ES6 classes. You can define them using a function name, followed by a list of parameters in a pair of parenthesis (para1, …, paramN) and a pair of curly braces { … } that delimits the body statements.

Answer 19

Shorthand method

Question 20

3 properties of arrow functions

Answer 20

1. The arrow function does not create its own execution context, but takes it lexically
2. The arrow function is anonymous: name is an empty string
3. arguments object is not available in the arrow function

Question 21

RETURNS AND WHY?

class Numbers {  
  constructor(array) {
    this.array = array;
  }
  addNumber(number) {
    if (number !== undefined) {
       this.array.push(number);
    } 
    return (number) function () { 
      this.array.push(number);
    };
  }
}
var numbersObject = new Numbers([]);  
numbersObject.addNumber(0);  
console.log(numbersObject.array)

Answer 21

error

function is NOT a arrow function

Question 22

Without the arrow function is necessary to manually fix the context. It means adding fixes by using ______ method:

Answer 22

.bind()

Question 23

ECMAScript 6 improves this usage by introducing the __________, which takes the context lexically. This is nice, because from now on is not necessary to use .bind(this) or store the context var self = this when a function needs the enclosing context.

Answer 23

arrow function

Question 24

The __________ in JavaScript returns a_______ object. Its syntax is similar to function expression, function declaration or method declaration, just that it requires a star character *.

Answer 24

generator function

Generator

Question 25

WHAT TYPE OF FUNCTION?

function* indexGenerator(){  
  var index = 0;
  while(true) {
    yield index++;
  }
}

Answer 25

Generator

Question 26

x=>x*2

write as a regular function declaration

Answer 26

function (x) {
return x * 2;
}

Question 27

what scope is “VAR”?

Answer 27

function scope

Question 28

what scope is “LET”

Answer 28

block scope

Question 29

function sum1(a, b) {  
  return a + b;
}
var sum2 = function(a, b) {  
  return a + b;
}
var sum3 = (a, b) => a + b;  
console.log(typeof sum1 === 'function'); // =>

Answer 29

true

Question 30

function sum1(a, b) {  
  return a + b;
}
var sum2 = function(a, b) {  
  return a + b;
}
var sum3 = (a, b) => a + b;  
console.log(typeof sum3 === 'function'); // =>

Answer 30

true

Question 31

function setupWhatever (){
  console.log(x)
  var x = 3;
  console.log(x);
}

setupWhatever();

//returns?

Answer 31

undefined

3

Question 32

function setupWhatever (){
  console.log(x)
  let x = 3;
  console.log(x);
}

setupWhatever();

//returns?

Answer 32

syntax error.

let cannot be defined after

Question 33

function setupWhatever (){

  let x;
  console.log(x);
  x = 3;
  console.log(x)
}

setupWhatever();

Answer 33

undefined

3

Question 34

what is block scope

Answer 34

anything in between curly brackets, if, for….

Question 35

function setupWhatever (){

for (var x = 1; x < 100; x++){

}
console.log(x);
}

setupWhatever();

Answer 35

100

Question 36

function setupWhatever (){

for (let x = 1; x < 100; x++){

}
console.log(x);
}

setupWhatever();

Answer 36

error.

Question 37

One possible application of _______ is a better way to access the global object in a browser or NodeJS script:

Answer 37

new Function

Question 38

The functions created this way don’t have access to current scope, thus closures cannot be created. They are always created in the global scope.

Answer 38

new functions

Question 39

If the function should use this from the enclosing function, the________ function is a good solution. When the callback function has one short statement, the function is a good option too, because it creates short and light code.

Answer 39

arrow

Question 40

________ way to declare functions generally should not be used. Mainly because it opens potential security risks, doesn’t allow code auto-complete in editors and lose the engine optimizations

Answer 40

new Function

Question 41

with JS a outside variable is or is not available inside a function

Answer 41

is